Reconsideration of injury criteria for pedestrian subsystem legform test~Problems of rigid legform impactor 2001-06-0206
The legform impactor proposed by EEVC/WG17 is composed of a
rigid thigh segment and a rigid lower leg segment. Human bone,
however, has flexibility, causing some differences between the EEVC
rigid legform impactor and the human leg. This research analyzes
the influence of the differences (rigid versus flexible) on the
injury criteria. It also reanalyzes the upper tibia acceleration
with regard to the fracture index.
The rigid legform impactor cannot simulate bone bending motion,
so the injury criteria should consider the legform rigidity. It
means the injury criteria need to include the bone bending effect.
From several PMHS test results, the shearing displacement becomes
23 mm and 20 degrees for bending angle including the bone bending
effect. However, the bone bending effect will change with the
loading conditions. Therefore, to establish a certain injury
criteria for a rigid legform impactor is impossible. To solve this
problem, a flexible legform impactor seems to be needed. If a
flexible legform impactor exists, the relationship between rigid
bone and flexible bone need not be considered, and the pure
ligament tolerance can be applied.
The threshold of upper tibia acceleration as for lower leg
fracture (fibula/tibia/tibia+fibula fracture) was found to be 198G
for 50% injury risk, but if we focus on the tibia fracture
(tibia/tibia+fibula fracture), exclude the fibula- only fracture
cases, the threshold becomes 247G.
By the way, to use only the upper tibia acceleration as the leg
fracture index is a problem. The relationship between upper tibia
acceleration and fracture was obtained from a PMHS test series
which were conducted normal bumper height, but if the impact point
is changed, the upper tibia acceleration becomes lower but the leg
fracture occurs. Therefore, if the acceleration use for the leg
fracture index, the accelerometer should be attached proper
position. More the worse, the tibia acceleration from the rigid
impactor is completely different from human leg because of its
rigidity. Therefore, the acceleration from a rigid legform impactor
should not be used for the estimation. If the legform impactor is
flexible, the acceleration becomes proper, and can be made proper
Finally, a flexible legform impactor seems to be needed for
proper estimation of leg injury.